Active learning ideas
This topic investigates the 'fire-born' rocks, focusing on the journey from molten magma to solid crystalline structures. Students explore how the environment of cooling, whether deep underground or on the surface, dictates the texture and grain size of the resulting rock. This is a fundamental part of the OCR Geology specification, requiring students to classify rocks like granite, basalt, and gabbro based on their mineralogy and cooling history.
Activity 01
Using salol (phenyl salicylate) on warm and cold microscope slides, students observe crystal growth in real-time. They record how the speed of cooling directly impacts the size of the crystals formed, mimicking intrusive and extrusive environments.
How does cooling rate affect the texture of igneous rocks?
Activity 02
Groups are given cards representing different minerals. They must arrange them in the order they crystallise from a melt (Bowen's Reaction Series) and then predict which minerals will be found together in mafic vs. felsic rocks.
What is the difference between mafic and felsic magmas?
Activity 03
Display samples showing vesicular, porphyritic, glassy, and phaneritic textures. Students move between stations to sketch the textures and hypothesize the specific volcanic or plutonic events that created them.
How do intrusive and extrusive environments shape rock formation?
A few notes on teaching this unit
Watch Out for These Misconceptions
Magma and lava are the same thing.
Magma is molten rock below the surface; lava is molten rock that has erupted. This distinction is crucial because the presence of volatiles (gases) and the cooling rate differ significantly between the two. Using a 'bottled soda' analogy helps explain the role of pressure and gas release.
All igneous rocks are formed from volcanoes.
The majority of igneous rocks (plutonic) form deep underground and are only seen after millions of years of erosion. Comparing the volume of batholiths to volcanic cones in a visual diagram helps correct this surface-level bias.
Methods used in this brief
Mineral Identification and Properties
Develop practical skills in identifying common rock-forming minerals using diagnostic physical properties. Students will investigate hardness, cleavage, lustre, and specific gravity.
8 methodologies
Sedimentary Environments
Trace the journey of sediments from weathering and erosion to transport, deposition, and lithification. Analyse sedimentary structures to interpret past depositional environments.
8 methodologies
Metamorphism and Metamorphic Rocks
Investigate the changes in rocks subjected to high heat and pressure without melting. Differentiate between contact and regional metamorphism and their resulting rock types.
8 methodologies